1. Field of the Invention
Embodiments of the present invention generally relate to a telemetry operated circulation sub.
2. Description of the Related Art
A wellbore is formed to access hydrocarbon bearing formations, e.g. crude oil and/or natural gas, by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a tubular string, such as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on a surface platform or rig, and/or by a downhole motor mounted towards the lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore. An annulus is thus formed between the string of casing and the formation. The casing string is temporarily hung from the surface of the well. The casing string is cemented into the wellbore by circulating cement into the annulus defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
While drilling, it is advantageous to have a downhole sub, known as a circulation sub, that allows drilling fluid to be diverted on demand from the drill string bore to the annulus in order to facilitate operations, such as hole cleaning. Prior art circulation subs are operated by dropping a closure member, such as a ball or dart. These subs are problematic due to the time required for the closure member to reach the sub from surface and reliability issues encountered once the closure member reaches the sub.